With regard to personal authentication using a fingerprint, various systems have so far been developed which, instead of the old-established method involving visual inspection, a laser, etc. is used and a pattern is inputted into a computer as an image and analyzed. A large number of techniques for a sensor section for detecting a fingerprint have been proposed; for example, an optical method in which a fingerprint pattern is directly captured into an image sensor by combining differences in scattering angle between peak and valley with total reflection conditions, and a method in which a pattern is extracted by utilizing a semiconductor sensor that detects differences in charge distribution on a contact face have been put into practice. Furthermore, a method in which personal authentication is carried out by extracting a vein pattern of a finger-tip or a palm of a hand by means of near-infrared light has been proposed, and commercialization thereof is underway. However, none of these methods is yet perfect, and the fight against forgery is continuing.    (Patent Publication 1) JP-A-5-73666 (JP-A denotes a Japanese unexamined patent application publication)    (Patent Publication 2) JP-A-8-16752    (Patent Publication 3) JP-A-2003-331268
On the other hand, it is known that, when a laser is shone on a living body, the intensity distribution of reflected scattered light forms a dynamic laser speckle (random spot pattern) due to moving scattering particles such as blood cells; this pattern is detected on an imaging plane by an image sensor, and by quantifying changes over time of the pattern in each pixel and displaying them as a map, it is possible to image the blood flow distribution of capillary vessels in the vicinity of the surface of the living body. Using such a phenomenon, techniques and devices for measuring a blood flow map of the area underneath the skin or of the ocular fundus have been proposed by the present inventors.    (Patent Publication 4) JP-B-5-28133 (JP-B denotes a Japanese examined patent application publication)    (Patent Publication 5) JP-B-5-28134    (Patent Publication 6) JP-A-4-242628    (Patent Publication 7) JP-A-8-112262    (Patent Publication 8) JP-A-2003-164431    (Patent Publication 9) JP-A-2003-180641
The present inventors have carried out an intensive investigation into the concept of combining a blood flow map and a fingerprint pattern and its use for personal authentication, and have already proposed a personal authentication method involving measuring subcutaneous blood flow and means therefor. That is, there have been proposed a personal authentication method comprising (1) a step of imaging, on an image sensor as a laser speckle using an optical system, light reflected from a subcutaneous blood vessel layer when a laser beam is expanded and made to irradiate a finger pad, (2) a step of determining a quantity that represents the rate of a change with respect to time of the amount of light received for each pixel of the laser speckle, for example, the average rate of change with respect to time, or the reciprocal of the magnitude of the variation in the amount of light received integrated over the exposure time of the image sensor, and obtaining a finger pad blood flow map as a two-dimensional map of numerical values thereof, and (3) a step of comparing and evaluating a fingerprint pattern represented as a blood flow map against pre-registered data of individuals, and devices for carrying out each step (Patent Publication 10).    (Patent Publication 10) International Patent Application WO2005/122896
It has been found that, since fingerprint patterns have complicated shapes compared with vein patterns, the methods and devices for personal authentication in the above-mentioned proposals can achieve authentication with considerable accuracy. However, there is a possibility that more sophisticated crimes such as, for example, smoothing a fingerprint using a chemical, etc., and affixing thereto a thin sheet having projections and recesses imitating a fingerprint of another person, cannot be prevented sufficiently. It is thus necessary to develop a more stringent personal authentication method and device for applications where more powerful prevention of crime is necessary.